1. Field of the Invention
In a control system for controlling a controlled system activated by a plurality of actuators, the present invention relates to a control system and an optimality decision unit which define optimum controlled variables of individual actuators by synthetically judging the operation of the above described controlled system and a plurality of actuators.
2. Description of the Related Art
In control units of the prior art, control is effected by using a plurality of output signals representing the operating state of the controlled system. In such a scheme that individual outputs are observed to effect control, control becomes local and optimality of the overall system cannot be considered, resulting in a drawback.
In recent years, therefore, it is demanded to derive the overall optimality by using a plurality of signals. By using a rolling mill system, which is so complicated that a single control unit may not control it, as the controlled system, for example, operation of a conventional control unit and a conventional control method will now be described.
From the viewpoint of improvement in quality and productivity of products, improvement in precision of shape control is keenly demanded for a rolling mill which rolls a material to be rolled. In a multistage rolling mill, the shape control of the rolled material is performed by three kinds of control, i.e., control of a work roll bender, an intermediate roll bender and an intermediate roll shifter. Even if the rolled material is a hard material such as stainless steel, a product having a shape which is satisfactory to some degree can be obtained by the above described shape control as described in "Hitachi Review", Vol. 70, No. 6, (June 1988), pp. 81 to 86. In the above described three kinds of shape control, however, a local shape defect such as local elongation caused in the rolled material by deformation of work rolls cannot be corrected. Deformation of rolls is caused by frictional heat and plastic working heat, and it is typically referred to as thermal crown. For correction of local shape defect, it is considered that shape control using coolant control, in which coolant is injected into the work rolls, is effective. The shape control using coolant control is already put into practical use.
However, physical characteristics of rolling largely change depending upon various factors. Even if control is effected by making a control model in the vicinity of a particular operation point, therefore, the model diverges from the actual operation of the rolling mill in many cases. As a result, feedback control, which brings about a fine result if the model is accurate, cannot fully demonstrate its ability and cannot exceed a skilled operator who manipulates the rolling mill in accordance with intuition and experience, resulting in a problem.
In the above described art, attention was not paid to making the best use of know-how of skilled operators and there was a problem of control performance.